The object of the proposed research is to identify the fast, time- dependent steps by which hormones interact with carrier proteins, metal ions, and receptor sites. These interactions will be studied by adapting the mathematical techniques of relaxation kinetics to hormone systems. The relaxation kinetics of hormone-binding will be studied using a stopped-flow temperature jump spectrometer in three prototype systems: a) the neurophysin-oxytocin system, which consists of a peptide hormone and its binding protein, b) the estradiol-alpha-fetoprotein system, which consists of a steroid hormone and its binding protein, and c) the oxytocin-uterine system, as a hormone-receptor model. Little information exists on the time-dependent events which occur. And, in the final analysis, hormone action can only be clarified by understanding the sequence of events in the complete time-ordered series. We propose to mate the endocrinology of hormone action with the physical chemistry of relaxation kinetics to begin to answer these questions.